Resonant routing of optical pulses in coupled-cavity structures

摘要

The transmission properties of side-coupled circular cavity systems are studied based on numerical two-dimensional finite-difference time domain modeling. The spatial asymmetry is introduced due to different separations between the circular resonators and side-coupled stripe waveguides. These structures can be viewed as 4-port routers where different ports are connected due resonant coupling between the guided modes in stripe-waveguides and whispering gallery modes in circle resonators. It is found that due to strongly asymmetric geometry, significant optical losses, and mode conversion processes, such structures display strongly asymmetric optical transmission properties for the waves propagating in forward and backward directions between the ports. In non-optimized single microcavity structures, it results in isolation ratios on the order of 10 dB for wavelengths resonant with WGMs. In structures formed by two closely spaced circular resonators, WGMs are strongly coupled leading to formation of bonding and antibonding photonic molecular modes. It is shown that at the wavelengths resonant with hybridized molecular modes the isolation ratios can be increased beyond 20 dB. At the same time, different wavelengths can be preferentially coupled to different ports resulting in wavelength demultiplexing functionality.